In recent years, there has been known a coordinate measuring instrument for measuring various shapes such as an outer diameter, an inner diameter of a hole and a center position of the hole of a work, which is rested on a mount, and has become increasingly common and is widely used for the measurement and the like of a tridimensional object with high accuracy.
The general construction of the coordinate measuring instrument of the type described has heretofore been one as shown in FIG. 3 for example. More specifically, in FIG. 3, a pair of supports 3 are erected from a mount 2 formed of a stone surface plate or the like rested on a support base 1, a transverse member 4 made smoothly movable by an air bearing or the like in the longitudinal direction, i.e. the direction of Y-axis is mounted onto these supports 3, and a relative movement value between the transverse member 4 and one of the supports 3 is detected by a Y-axis displacement detector 5 comprising an optical displacement detector or the like.
A slider 6 is provided on the transverse member 4 in a manner to be made smoothly movable by an air bearing or the like in the lateral direction, i.e. the direction of X-axis, and a relative movement value between this slider 6 and the transverse member 4 is detected by an X-axis displacement detector 7 comprising an optical displacement detector or the like. A square shaft-shaped spindle 9 provided at the bottom end thereof with a measuring element 8 is supported by the slider 6 in a manner to be made slidable by an air bearing or the like in the vertical direction, i.e. the direction of Z-axis, and a relative movement value between this spindle 9 and the slider 6 is detected by a Z-axis displacement detector 10 comprising an optical displacement detector similar to the above-mentioned detectors. Here, the transverse member 4, the slider 6 and the spindle 9 constitute a measuring element support member 11. In consequence, the measuring element 8 is supported by the measuring element support member 11, and the measuring element 8 is supported in a manner to be made movable relative to a work 12 to be measured, which is rested on the mount 2, tridimensionally, i.e. in the directions X-, Y- and Z-axes.
With the above-described arrangement, a shape or the like of the work 12 is measured such that: a spindle 9 is manually grasped, or gripped by a hand of a robot in the case of an automatical measurement, and the measuring element 8 is brought into contact with a preset origin to obtain a reference of polar coordinates; subsequently, the measuring element 8 is brought into contact with measuring points of the work 12 and the relative movement values of this measuring elements from the origin in the directions of X-, Y- and Z-axes are measured by the detectors 5, 7 and 10; and signals from the detectors 5, 7 and 10 are suitably processed by a processing unit comprising a computer or the like, not shown, to thereby obtain measured values.
Now, in the coordinate measuring instrument of the type described, to achieve the measurement with high accuracy, constructions of various portions are formed solidly, and the measuring element 8 is integrally secured to the measuring element support member 11, at a predetermined distance therefrom. In consequence, the conventional coordinate measuring instrument presents the following disadvantages.
(1) In order to move the measuring element 8 to a desired measured surface of the work 12, the measuring element 8 should necessarily be moved together with a moving mechanism as a whole, i.e. the measuring element support member 11, and moreover, depending on the shape of the work 12, the measuring element should be moved, making a detour around the work 12. Thus, the working efficiency becomes low, and further, there is a possibility of causing damages to the measuring element 8 due to a collision of the measuring element during the detour.
(2) As in the case where the work 12 has a protruding portion and a portion formed at the undersurface of this protruding position is measured, there may occur a surface to be measured, against which the measuring element 8 cannot abut or cannot easily abut. In such cases, deliberate works may be required or works of remounting the work 12 for change in its posture may be needed.
(3) As in the case of measuring the dimension of a hole, where the thickness or position does not matter much, but only the diameter of the hole is objected, the portions to be measured include many points not requiring a positioning in the absolute coordinate system, i.e. the distance from the origin, however, all of these measurements are carried out by moving the measuring element 8 tridimensionally in the same manner as in the conventional example.
As described above, all of the above-described disadvantages lower the working efficiency. As the scope of application to objects to be measured is expanded and the shapes of the objects become complicated, these disadvantages have become important factors to impede the spread of the coordinate measuring instrument unless these disadvantages are obviated.
Additionally, the coordinate measuring instruments need not necessarily be limited to the shape shown in FIG. 3 and have various types including one in which gate-shaped columns are slidably mounted on the mount, one in which the measuring element support member is formed into a cantilever beam shape, and further, one in which the mount is made movable in the direction of Y-axis. However, the above-described disadvantages are common to the coordinate measuring instruments of all types.
The present invention has as its object the provision of a coordinate measuring instrument wherein the measurement suitable for the characteristics of the portion to be measured of the work can be performed and the measuring efficiency can be highly improved.